DESCRIPTION:(adapted from applicant's abstract) The peptide, corticotrophin releasing factor (CRF), mediates the stress response. CRF is present in the cerebellum, contained in climbing and mossy fibers, where its role is presently unknown. Previous studies have focused on the distribution, physiology and developmental expression of CRF in the cerebellum. To date, two major types of CRF receptors, CRF-R1 and CRF-R2, have been identified. Previous in situ hybridization studies of cerebellum have shown the presence of mRNA for CRF-R1, but not CRF-R2. However, preliminary data from the applicant reveals immunostaining for both receptors in cerebellum. The applicant thus hypothesizes that CRF-R1 is located postsynaptically and CRF-R2 presynaptically, on cerebellar afferents and further, that changes in the firing rate of cerebellar afferents that contain CRF will modulate the expression of CRF and its two receptor subtypes. A major focus of the applicant's previous research has been on the role of CRF in development. They postulate that there will be a differential temporal and cellular expression of the two receptor subtypes during embryonic and neonatal development which is further modified as the animal matures and further hypothesize that CRF acts as a neurotrophic factor during development. The proposal has 4 specific aims: 1) to analyze the cellular distribution of CRF-R1 and CRF-R2 receptors in the adult cerebellum using light and electron microscopic immunocytochemical visualization, 2) to determine how altering the firing rate and pattern of CRF-containing afferents by electrical stimulation alters CRF and CRF receptor expression, 3) to analyze the changes in the cellular distribution of CRF receptors during postnatal development and 4) to evaluate potential trophic effects of CRF on cerebellar neurons in culture.